Methods and apparatus for relatively invariant input-output spectral relationship amplifiers

ABSTRACT

An electronic amplifier delivers to a load an output signal related to an input, typically with increased power. As the power output, volume, or gain of the amplifier is changed, so may the spectral characteristics of the signal. In order to maintain the desired spectral or tonal character of the output signal over the dynamic range of output power, biasing of the amplifier must be adjusted. Particular ratios of drive and bias currents and/or voltages for different implementations of amplifier technologies should be relatively constant to produce substantially invariant input-output spectral relationships from low power output through high power output settings. Several techniques are presented which provide these relationship in amplifiers.

FIELD OF THE INVENTION

Embodiments of the present invention relate to amplifiers that retainthe power amplifier spectral characteristics over a wide range of outputpower.

BACKGROUND OF THE INVENTION

An electronic amplifier (amplifier, amp) is an apparatus that enables aninput electrical signal to control power from a source independent ofthe signal and thus is capable of delivering an output that bears somerelationship to, and is generally greater than, the input signal. Anamplifier may be designed for a specific purpose. For example, radiofrequency (RF) amplifiers may convert low-power signals with frequenciesgenerally in the portion of the electromagnetic spectrum between audioand infrared into a larger signal with more power, typically for drivingthe antenna of a transmitter. In another example, an audio amplifier mayamplify audio signals (e.g., signals in the range of human hearing) to asuitable level (magnitude) for driving loudspeakers or other devices. Aguitar amplifier is another example of an amplifier designed for aspecific purpose. A guitar amplifier is designed to amplify theelectrical signal of guitar or an acoustic pickup.

An amplifier may strive to reproduce the electromagnetic spectrum (e.g.,spectral characteristics, frequencies, tone) of the input signal.Alternatively, the amplifier may alter the spectrum of the input signal.The output spectrum may depend on the output power level (magnitude).For example, a guitar amplifier may add effects such as distortion athigh output power levels. A musician may find these effects desirable.However, guitar amplifiers may fail to reproduce the same effects atlower output power. For example, a musician using a guitar amplifier ina concert hall or arena setting with a high power output may desire tohave the same effects at a lower output power while playing in a smallerroom or location. Maintaining the relationship of input to outputspectrum over the dynamic range (the ratio between the largest andsmallest possible values) of output power may not be achievable withtypical amplifiers.

In other examples, it may be desirable for audio amplifiers tofaithfully reproduce the electromagnetic spectrum of the input signal atthe output regardless of output power levels. Audio amplifiers thatintroduce distortion or other effects alter the original spectrum (e.g.,sounds) which listeners may find objectionable. In this example, it isdesirable to maintain the relationship of input spectrum to outputspectrum over the dynamic range of output power without distortion.

Electronic amplifiers that maintain a desired relationship of inputspectrum to output spectrum over the dynamic range of output powersalleviate the problem of power output dependent spectral variations.Thus, maintaining a spectral relationship between an input and outputsignal in an amplifier is a need felt by many users across multiplefields.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will be described with reference tothe drawings, wherein like designations denote like elements, and:

FIG. 1 is a functional block diagram of an apparatus to amplifyelectrical signals in accordance with various aspects of the presentinvention;

FIG. 2 is a functional block diagram of the amplifier of FIG. 1 foraudio signals in accordance with various aspects of the presentinvention;

FIG. 3 is a schematic diagram of a circuit of a fixed bias poweramplifier of the audio amplifier of FIG. 1;

FIG. 4 is a schematic diagram of a circuit showing a voltage regulatorbiasing of the amplifier of FIG. 2;

FIG. 5 is a schematic diagram of a circuit of an implementation of thevoltage regular bias of FIG. 4 according to various aspects of thepresent invention;

FIG. 6 is a schematic diagram of the circuit of FIG. 4 showing atracking control grid bias;

FIG. 7 is a schematic diagram of a circuit showing an implementation ofa tracking control grid bias of FIG. 6 according to various aspects ofthe present invention;

FIG. 8 is a schematic diagram of a circuit of FIG. 6 showing a phasesplitter bias;

FIG. 9 is a schematic diagram of a circuit of FIG. 8 showing a controlgrid phase splitter bias according to various aspects of the presentinvention; and

FIG. 10 is a schematic diagram of FIG. 8 showing a phase splitter with avoltage controlled differential amplifier according to various aspectsof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A signal is used to convey information. An electrical signal may becharacterized by voltage (e.g., electromotive force), current (e.g.,flow of electric charge), electromagnetic waves (e.g., spectrum,frequencies, wavelengths, tones), power (e.g., rate of transferring ortransforming energy), and/or other quantities. As used herein, the term“signal” means an electrical signal that conveys information.

An amplifier boosts (e.g., enlarges, magnifies, increases, raises,gains) one or more characteristics (e.g., voltage, current, power) ofone or more signals. Amplifiers may have unity gain (e.g., noamplification). Amplifiers may also attenuate a signal. Amplifiers maybe designed for particular applications (e.g., guitar amplifier),frequencies ranges (e.g., audio amplifier, radio frequency amplifier),and/or to boost particular characteristics (e.g., current amplifier,voltage amplifier, differential amplifier, inverting amplifier,integrating amplifier). As used herein, the term “amplifier” or “amp”means any electrical or electronic equipment that amplifies one or morecharacteristics of a signal.

An amplifier may include a preamplifier (pre-amp or preamp), a phasesplitter, a power amplifier, and a power supply (FIG. 1). An amplifiermay also include a tone stack and a transformer (FIG. 2). A pre-amp mayelectrically couple (e.g., establish an electrical connection, establisha path for current to flow) to a low-level input signal (source). Thecomponents of an amplifier may be contained in a single enclosure (e.g.,housing, box, assembly, case). The components may be contained inmultiple enclosures with any combination of components in eachenclosure.

A pre-amp may present a suitable impedance (e.g., matched impedance) toa signal source. A pre-amp may provide gain (e.g., amplification) to theinput signal to produce a signal suitable for further processing. A userinterface may be provided to a user to adjust the gain of the pre-amp. Apre-amp may provide suitable output impedance to a component for furtherprocessing. A pre-amp may provide equalization and/or mixing of theinput signal. A pre-amp may produce distortion in a signal. A pre-ampmay contain any combination of conventional circuit elements (e.g.,electron tubes, semiconductors, integrated circuits, transistors,resistors, capacitors, inductors, transformers) to perform thesefunctions. A pre-amp may be omitted (e.g., left out, not included) froman amplifier if its function is performed by another component or if itsfunction is not required.

A phase splitter may electrically couple to a pre-amp to provide furtherprocessing. A phase splitter may produce one or more signals from aninput signal which differ in phase (e.g., different polarities,quadrature signals) from one another. A phase splitter may provide asuitable impedance for an input and/or an output circuit coupled to thephase splitter. For example, a phase splitter may separate an inputsignal into two signals with opposite polarities for further processingby a push-pull amplifier circuit. In another example, a phase splittermay produce a single signal for further processing by single phaseamplifier. A phase splitter may be omitted from an amplifier if only asingle phase of the signal is required for further processing. A phasesplitter may contain any combination of conventional circuit elements toperform these functions.

A power amplifier amplifies an input signal to a sufficient power level(magnitude) to drive a load (e.g., utilization device, antenna,loudspeaker, circuit that consumes electric power). A load may be one ormore devices. A device that provides additional processing may be aload. A power amplifier may be the last stage in an amplifier before aload. A user interface may be provided to a user to adjust an amount ofpower output by the power amplifier. A power amplifier may employ anyclass of operation or service (e.g., Class A, Class AB, Class C, ClassD). The signal output by the power amplifier may include distortion(e.g., harmonic distortion, crossover distortion). The output of thepower amplifier may be proportional to the input signal (e.g., linear).There may be a non-linear relationship between the output of the poweramplifier and the signal input to the power amplifier. A power amplifiermay contain any combination of conventional circuit elements to performthese functions.

A power supply includes a supply of energy. Energy may be used forenabling the operation of electronic circuits (e.g., devices) such as anamplifier, processing circuit, and/or a user interface. A power supplymay include any conventional component for providing energy such as abattery, a transformer that transforms line power, and/or a capacitor. Apower supply may store energy for providing energy. Energy from a powersupply may be used as a force (e.g., voltage, current) for an amplifieras discussed herein.

Tone refers to the pitch, quality, and strength of musical or vocalsounds. A tone stack may output a processed input signal that has beenmodified in accordance with a user interface. A tone stack may provide auser interface to adjust a frequency response (e.g., the quantitativemeasure of the output spectrum) of an input signal. A tone stack mayadjust timbre (e.g., tone color, tone quality) of an audio signal. Theuser interface may provide for user adjustment of treble (e.g., tones atthe higher range of human hearing), bass (e.g., tones at the lowerfrequency or range of human hearing), and/or middle (e.g., tones at themidrange of human hearing). A tone stack may allow a user to controlequalization, reverberation, and/or mixing of the input signal. A tonestack may provide an effects output port (e.g., connection, socket,plug) and an effects input port for an external device to connect. Theexternal device may provide modification (e.g., additional effects) tothe signal from the effects output port and return the modified signalto the effects input port of the tone stack. A tone stack may containany combination of conventional circuit elements to perform thesefunctions.

A transformer may provide impedance matching of an amplifier output toan impedance of a load. A transformer may provide galvanic isolation(e.g., blocking of direct current). A transformer may providealternating current restoration (e.g., converting direct current in atransformer primary winding to alternating current in the transformersecondary winding). Impedance matching may maximize the power transferfrom an amplifier to a load. Impedance matching may minimize a signalreflection from a load. A transformer may provide a center tap forconnecting to a bias voltage. A transformer may provide connections towinding ends to accept output signals from a power amplifier. Atransformer may contain any combination of conventional circuit elementsto perform these function.

A user interface may include electronic devices (e.g., switches, pushbuttons, touch screen, potentiometers, rheostats, wireless transceiver,remote controls) for receiving information (e.g., data) from a user. Auser may manually manipulate one or more electronic devices of a userinterface to provide information. Electronic devices for receivinginformation from a user may include a wireless receiver that receivesinformation from an electronic device (e.g., smartphone, tablet, watch).A user may manually provide information to a user interface via anelectronic device. A user interface may include electronic devices forproviding information to a user. A user may receive visual and/orauditory information from a user interface. A user may receive visualinformation via devices (e.g., LCDs, LEDs, light sources, graphicaland/or textual display) that display information. A user interface mayinclude a wireless transmitter for transmitting information to anelectronic device for presentation to a user.

For example, amplifier 100, shown in FIG. 1, includes pre-amp 120, phasesplitter 140, power amplifier 150, and power supply 160. Pre-amp 120electrically couples to an input signal and provides the functions of apre-amp as described above. Pre-amp 120 processes the input signal forfurther processing by phase splitter 140. The input of phase splitter140 electrically couples to the output of pre-amp 120. Phase splitter140 provides the functions of a phase splitter as described above. Theoutput of phase splitter 140 electrically couples to the input of poweramplifier 150. Power amplifier 150 provides the functions of a poweramplifier as described above. Power amplifier 150 electrically couplesto a load. Power supply 160 provides the energy required by pre-amp 120,phase splitter 140, and power amplifier 150. A user interface (notshown) may provide the user a means for controlling the amount of poweroutput from amplifier 100. A user interface may provide the user with ameans of controlling other characteristics and/or functions of amplifier100.

In another example, amplifier 200, shown in FIG. 2, includes input port210, pre-amp 220, tone stack 230, phase splitter 240, power amplifier250, transformer 260, loudspeaker 270, and power supply 280. Input port210 may provide an electrical connection for an input signal and couplesthat signal to an input of pre-amp 220. A gain (e.g., amplification,boost, volume, increase in power) of pre-amp 220 may be set via a userinterface. Pre-amp 220 performs the functions of a pre-amp on the inputsignal as described above. Tone stack 230 couples to pre-amp 220 andtakes as an input the signal output by pre-amp 220. A user may adjust(e.g., modify, alter) the tonal qualities (e.g., timbre, bass, treble,midrange, reverberation) of the signal processed by tone stack 230 via auser interface. Tone stack 230 performs the function of a tone stack asdescribed above and outputs a signal for phase splitter 240. Phasesplitter 240 couples to tone stack 230 and performs the function of aphase splitter as described above. Phase splitter 240 may separate asignal into one or more phases to be processed by power amplifier 250.

Power amplifier 250 couples to phase splitter 240 and receives thesignal output by phase splitter 240. The output power of the signal frompower amplifier 250 may be controlled through a user interface. Poweramplifier 250 may provide distortion (e.g., harmonics, crossover) to thesignal. Power amplifier 250 performs the function of a power amplifieras described above.

Power amplifier 250 may be a push pull amplifier which has an outputstage that can drive a current in either direction through a load. Theoutput stage of a typical push pull amplifier may include at least oneelectron tube (e.g., vacuum tube, receiving tube, gas tube). Electrontubes for amplifiers may be conventional amplifier tubes (e.g., triode,tetrodes, pentodes). The output stage may include at least onesemiconductor device (e.g., transistor, BJT, FET). Bipolar junctiontransistors (BJTs or bipolar transistors) are devices that rely on thecontact of types of semiconductor (e.g., PNP, NPN) for its operation.Field-effect transistors (FETs) use an electric field to control theshape and therefore the conductivity of a channel of one type of chargecarrier in a semiconductor. FETs may be junction field-effecttransistors (JFETs), metal oxide semiconductors (MOSFETs) or any otherconventional FET transistor.

A push pull amplifier may operate in a particular class of service(e.g., Class A, Class B, Class AB) with any of the devices describedabove (e.g., electron tube, BJT, FET). The class of service may bechanged by altering the bias parameters of a device.

Transformer 260 couples to, and receives a signal from, power amplifier250. Transformer 260 provides a matching impedance to loudspeaker 270.Transformer 260 provides the function of a transformer as describedabove. Transformer 260 may provide galvanic isolation. Transformer 260may provide alternating current restoration.

Power supply 280 provides a source of energy for pre-amp 220, tone stack230, phase splitter 240, power amplifier 250, and transformer 260. Powersupply 280 performs the function of a power supply as described above.

The components of amplifier 200 may be contained within a single housing(e.g., enclosure, cabinet). A plurality of housings may contain anycombination of components, each housing electrically coupled to anotherhousing to provide the electrical connections between componentsdescribed above.

Power amplifier 302 in FIG. 3 provides an example of a push pullamplifier performing the functions of power amplifier 250. The outputstage in this example uses two pentode electron tubes, tubes 310 and314. The suppressor grids of tubes 310 and 314 are connected to theirrespective cathodes which are in turn connected to the circuit ground.The suppressor grids may be connected to a biasing circuit with anycombination of resistors, capacitors, diodes, or other conventionalcircuit elements. The heater connections to a power supply are notshown. VB+ provides a fixed voltage through a center tap of transformer360 to the plates of tubes 310 and 314. VB+ also provides a fixedvoltage, filtered through RFLTR and CFLTR, with current limited by RSG1and RSG2, to the screen grids of tubes 310 and 314, respectively. Phasesplitter 340 provides two signals to the input of power amplifier 302.The input signals are filtered by CDRV1 and RDRV1, which also providesAC (alternating current) coupling (e.g., capacitive coupling, blockingof direct current signals), to tube 310 and biased by fixed voltageVbias through RCG1 and RDRV1. Similarly, CDRV2 and RDRV2 providesfiltering and AC coupling, and RCG2 and RDRV2 with Vbias providesbiasing for tube 314. The biasing in this example is set (e.g.,predetermined, established) by a circuit designer.

For push pull Class AB 1 operation, the plate voltage, screen voltageand total zero signal plate current must be maintained in accordancewith tube 310 and 314 specifications. As an example, with a 6BQ5 (EL84)power amplifier pentode for tubes 310 and 314, plate and screen gridvoltages are 300 volts and total zero signal plate (quiescent) currentis 36 mA (milliamperes) per tube according to the manufacturer'sspecifications (e.g. data sheet, application note). The voltages andcurrent may be different for other tube selections. As the power outputor amplifier gains changes, tubes 310 and 314 may not remain within thedesign specifications for push pull Class AB1 operation.

In an embodiment of the present invention, power amplifier 402 in FIG. 4shows the use of a voltage regulator to supply a regulated voltage tothe screen grids of tubes 310 and 314. Regulator 420 may supply apredetermined voltage. Rcontrol may adjust the output voltage ofregulator 420 which, in turn, controls the output power. Regulator 420may automatically maintain a voltage level (typically within a ±5%output voltage tolerance) and thus may reduce unwanted voltagevariations (e.g., ripple, spiking). Voltage regulator 420 may beimplemented with a non-linear regulator. A linear regulator may be usedto implement the functions of regulator 420. Any combination ofconventional circuit components may be used to perform the functions ofvoltage regulator 420.

In other embodiments of the present invention, the voltage regulator maysupply a regulated voltage to the plates of tubes 310 and 314. Thevoltage regulator may supply a regulated voltage to the screen grids andplates of tubes 310 and 314.

Regulator 500 in FIG. 5 provides an example circuit of voltage regulator420. A convention linear voltage regulator (e.g., Microchip LR8 highinput voltage, adjustable 3-terminal linear regulator) may be used forregulator U51. Unregulated input power is supplied to the IN connection.The regulated output voltage is provided at the OUT connection. Theratio of R52 and R53 determines the output voltage level. The outputvoltage may be controlled via a variable resistance between the CONTROLconnection and circuit ground. Thus, the CONTROL input determines theoutput power of the power amplifier. Bypass transistor Q41 boosts thecurrent available through regulator 500.

In another embodiment of the present invention, power amplifier 602 inFIG. 6 includes control grid (CG) bias 630. CG bias 630 may follow acontrol law in which the output voltage is determined by the voltage atthe input at any given instant. The control law relationship may belinear or may be non-linear. CG bias 630 maintains a relationshipbetween a screen grid voltage and a control grid voltage on tubes 310and 314 while a constant plate voltage may be maintained. The tonalcharacteristics of an output audio signal are thus substantiallyinvariant (e.g., relatively constant, little or no change) when thescreen grid voltage changes because the bias voltage changes in acontrol law relationship to the screen grid voltage. By controlling theCG bias voltage, the zero-signal (quiescent) plate current can bemaintained according to the tube specifications.

As used herein, “substantially invariant” and “relatively invariant”when used with tonal characteristics or input-output spectralrelationships means that any change in the frequency composition of theoutput signal is imperceptible (e.g., unnoticeable, undetectable,indistinguishable, indiscernible) to an ordinary person listening to thesounds produced through a loudspeaker or that any change in frequencycomposition does not alter a result of any further processing of theoutput signal.

CG bias 700 in FIG. 7 is an example of a circuit to perform the functionof CG bias 630. Operational amplifier (OPAMP) U701 provides an inverted(e.g., opposite polarity) signal proportional to fixed reference voltageV715. The ratio of impedances R702 to R707 determines the gain of OPAMPU701. OPAMP U702 produces a signal proportional to the difference of anIN signal and the output from OPAMP U701. In general, the output ofOPAMP U702 may be the product of the impedance value of R704 with thesum of IN divided by the value of impedance R709 and the output voltageof OPAMP U701 divided by the impedance of R710. The resulting output ofOPAMP U702 follows a control law relationship to the IN input signal(the screen grid voltage). The functions of an operation amplifier maybe implemented with any combination of conventional electroniccomponents.

If U310 and U314 are both 6BQ5 (EL84) electron tubes, for example, andthe screen grid voltage changes from 300 volts to 100 volts while theplate voltage is maintained at 300 volts, the control grid voltage mustdecrease by 773 millivolts to maintain a zero signal (quiescent) platecurrent of 36 mA, as specified by the manufacturers for the particularclass of service. Thus, if a linear relationship is assumed, CG bias 700produces the following relationship:V_(CGB)=−0.053135V_(SGB)+4.54 Volts  Equation 1:

where V_(CGB) is the control grid bias voltage (output) and V_(SGB) isthe screen grid bias voltage (input).

The values of fixed reference voltage V715 and impedances R702, R704,R707, R709 and R710 may be appropriately selected to achieve therelationship in Equation 1 in this example. Capacitors C702 and C704 maybe included to provide low-pass filtering or may be omitted from CG bias700.

In another embodiment of the present invention, circuit 800 in FIG. 8includes a voltage controlled differential amplifier (VCDA) in phasesplitter 840. The VCDA is controlled by control law amplifier 850. Thecombination of amplifier 850 and VCDA may prevent the loss of dynamicrange of output power due to the control grid voltage of tube 310 and/ortube 314 becoming positive with respect to the cathode. A change in thepower amplifier class of service from Class AB1 to Class AB2 wouldresult in an electron tube grid voltage becoming positive with respectto the cathode. Amplifier 850 produces a signal in relation to thecontrol grid bias voltage of tubes 310 and 314 that, in turn, changesthe drive level within phase splitter 840.

An example of a circuit implementing a control law amplifier is shown inamplifier 900 in FIG. 9. OPAMP U901 produces a voltage proportional tofixed reference voltage V915. The voltage is proportional to the ratioof the values of impedances R902 to R907. OPAMP U902 produces a voltageproportional to the difference in voltage between an IN input signal andan output of OPAMP U901. The values of impedances R902, R904, R907,R909, and R910 determine the relationship of the voltage at output OUTto reference voltage V915 and the IN input voltage. The functions ofOPAMPs U901 and U902 may be implemented with any combination ofconventional electronic circuit components. OPAMPS U901 and U902 may beimplemented with integrated circuit operational amplifiers (e.g., TexasInstruments (TI) TL082, TI TL072, TI LF353).

An example of a circuit implementing a phase splitter with a VCDA isshown in phase splitter 1000 in FIG. 10. Transistors Q1001 and Q1002form a differential amplifier controlled by input VGB. Input voltage VGBdetermines the current through Q1002 and thus the cathode current intubes U1001 and U1002. In this example, tubes U1001 and U1002 are triodeelectron tubes arranged in a common cathode configuration (e.g.,long-tailed pair, differential pair). Phase splitter 1000 produces twooutput signals, DRIVE-A and DRIVE-B, with opposite polarities (e.g., 180degree phase difference) which may serve as inputs to power amplifiers302, 402, 602, and 802.

The differential amplifier in phase splitter 1000 may be implementedwith transistors as shown. The differential amplifier may be implementedwith operational amplifiers. Any combination of conventional electroniccomponents that performs the function of a VCDA may be used.

The functions of tubes U1001 and U1002 may be implemented with electrontubes. Transistors may be used to implement the functions of U1001 andU1002. Operational amplifiers may be used to implement the functions ofU1001 and U1002. Any combination of conventional electronic componentsthat perform the functions of U1001 and U1002 may be used.

Implementations of the present invention in an amplifier may includefixed or variable voltage regulator 420 of FIG. 4. Other implementationsof the present invention may include control law amplifier 850 and aVCDA of phase splitter 840. In still other implementations, an amplifiermay include fixed or variable voltage regulator 420, control lawamplifier 630, control law amplifier 850, and a VCDA of phase splitter840 of FIGS. 4-10.

The foregoing description discusses preferred embodiments of the presentinvention, which may be changed or modified without departing from thescope of the present invention as defined in the claims. Examples listedin parentheses may be used in the alternative or in any practicalcombination. As used in the specification and claims, the words‘comprising’, ‘including’, and ‘having’ introduce an open endedstatement of component structures and/or functions. In the specificationand claims, the words ‘a’ and ‘an’ are used as indefinite articlesmeaning ‘one or more’. When a descriptive phrase includes a series ofnouns and/or adjectives, each successive word is intended to modify theentire combination of words preceding it. For example, a black dog houseis intended to mean a house for a black dog. While for the sake ofclarity of description, several specific embodiments of the inventionhave been described, the scope of the invention is intended to bemeasured by the claims as set forth below. In the claims, the term“provided” is used to definitively identify an object that not a claimedelement of the invention but an object that performs the function of aworkpiece that cooperates with the claimed invention. For example, inthe claim “an apparatus for aiming a provided barrel, the apparatuscomprising: a housing, the barrel positioned in the housing”, the barrelis not a claimed element of the apparatus, but an object that cooperateswith the “housing” of the “apparatus” by being positioned in the“housing”.

What is claimed is:
 1. An apparatus for amplifying a first electricalsignal, the apparatus comprising: a phase splitter comprising at leastone device that separates an amplified first signal into one or moresecond signals, each second signal with a respective phase; a poweramplifier, comprising one or more electron tubes, that amplifies avoltage magnitude of the one or more second signals; wherein a biascurrent of the at least one device is provided by a voltage controlleddifferential amplifier; and the voltage control is proportional to acontrol law of a respective control grid voltage of the one or moreelectron tubes to maintain the spectral characteristics over a dynamicrange of output power.
 2. The apparatus of claim 1 further comprising avoltage regulator that supplies a regulated first voltage to arespective screen grid of the one or more electron tubes.
 3. Theapparatus of claim 2 wherein a second voltage in proportion to theregulated first voltage is supplied to a respective control grid of theone or more electron tubes whereby a desired amplifier class of serviceis maintained.
 4. The voltage regulator of claim 2 wherein a magnitudeof the regulated first voltage is user adjustable.
 5. The voltageregulator of claim 2 comprises a linear voltage regulator.
 6. The biascurrent of claim 1 wherein a set point of a magnitude of the currentfollows the control law of the control grid voltage to maintain adesired class of service over dynamic variations of a screen gridvoltage of the electron tubes.
 7. The bias current of claim 1 wherein aset point of a magnitude of the current is user adjustable.
 8. Theapparatus of claim 1 further comprising: a tone stack for adjustingtonal qualities of the amplified first signal; and a transformerelectrically coupled between the output of the power amplifier and anoutput load to match an impedance of the load and provide galvanicisolation.
 9. The apparatus of claim 1 further comprising apre-amplifier that amplifies a magnitude of the first electrical signal,wherein an output of the pre-amplifier electrically couples to an inputof the phase splitter.
 10. The device of claim 1 comprising one or moreelectron tubes.
 11. The device of claim 1 comprising one or more fieldeffect transistors.
 12. The device of claim 1 comprising one or morebipolar junction transistors.
 13. A method of amplifying an electricalsignal while maintaining the spectral characteristics of the signal overa range of power output, the method comprising: splitting the electricalsignal into one or more phases by a splitter; amplifying the splitelectrical signal with one or more electron tubes; setting a voltagecontrol proportional to a control law of a respective control gridvoltage of the electron tubes; supplying a bias current to the splitter,wherein a magnitude of the bias current is determined by the voltagecontrol; and maintaining a predetermined relationship between thecontrol grid voltage and the voltage control to retain the spectralcharacteristics of the amplified signal over a range of power outputlevels.
 14. The method of claim 13 further comprising controlling arespective screen grid voltage on the one or more electron tubes with aregulated magnitude of voltage.
 15. The method of claim 13 furthercomprising adjusting the respective control grid voltage on the one ormore electron tubes with a voltage proportional to a respective screengrid voltage.
 16. The method of claim 15 wherein the voltageproportional to the screen grid voltage for adjusting a control gridvoltage is variable.
 17. The splitter of claim 13 comprises adifferential amplifier.